Question

Two Catalyst switches, DSW1 and ASW1, are connected by a manually configured 802.1q trunk. Users in VLAN 1 on ASW1 can reach the network, but the switches log repeated '%CDP-4-NATIVE_VLAN_MISMATCH' messages every 60 seconds. On DSW1 the trunk port shows 'switchport trunk native vlan 99'; on ASW1 the same port shows 'switchport trunk native vlan 1'. Tagged VLANs 10 and 20 pass traffic correctly. What is the effect of this condition, and how should you resolve it?

Accepted Answer

Untagged frames can be leaked between VLAN 99 and VLAN 1, creating a potential VLAN-hopping risk; configure the same native VLAN on both trunk ends.

Answer

The trunk will go down; set both ends to 'switchport mode dynamic auto' so DTP renegotiates the native VLAN automatically.

Answer

Tagged VLANs 10 and 20 will be pruned; enable VTP pruning on both switches to restore connectivity.

Answer

The mismatch only affects CDP and is purely cosmetic; disable CDP on the trunk ports to stop the log messages with no other action needed.